We are currently looking to design a 18W offline flyback as follows:-
Currently I have done the design and have chosen to use UCC28C40D , and another design with UC3843.
-However, my boss believes the component count is too high and says we need a different solution.
-Please can I speak with Texas staff about our requirements?
Spec:
Vin = 85-265VAC
Vout1 = 36V +/-2V; 13W
Vout2 = 5V, +/-0.25V; 4W
Vout3 = 3.1V, +/- 0.3V; 0.6W
(Vout1,2,3 are fully SELV isolated outputs….not isolated from each other though)
Efficiency = 85%
Standby Power = <500Mw.
Frequency = 50-150KHz.
Skip-cycle during light load.
Capacitance on 36V Rail = 30mF.
(…..this is for energy storage for when there is a mains power cut when the customer is running fluid from the tanks….it closes the fluid flow off with the stepper motor valves)
-this 30mF capacitance should be charged up in ~ 1 second after power_ON……but we may allow this to extend up to say 3 seconds.
Notes on Standby:-
Our standby requirement is interesting, because during standby, our 5V & 3.1V rail is actually loaded with 170mW……..
….-this is due to the RF transceiver, which must keep listening for an ON command from the remote device during standby.)
High energy storage capacitance:
Most PWM controllers go into hiccup mode when charging up our big secondary capacitance. –and so are not useful to us
Anyway, myself and the R&D Engineering Manager, were wondering if you may have any suggestions to suit our requirement?
Schematic:
http://i52.tinypic.com/ab1ibt.jpg
……..please note that LT1243 is pin for pin compatible with our intended device, (UCC28C40D) from Texas
Here is the simulation file in LTSpice:-
http://www.2shared.com/file/zNwuM_u5/Matalan_SMPS_simulation__1_7__.html
my phone number is UK 07798 851534